Fan impeller structure of centrifugal fan

ABSTRACT

A fan impeller structure of centrifugal fan includes a hub, a first blade body set and a second blade body set. The hub has an extension section having a first side and a second side. The first blade body set is disposed on the first side, while the second blade body set is disposed on the second side. The first blade body set defines multiple first air inlets and multiple first air outlets. The second blade body set defines multiple second air inlets and multiple second air outlets. The first air outlets of the first blade body set or the second air outlets of the second blade body set are selectively arranged at unequal intervals so as to effectively reduce noise.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a fan impeller structure of acentrifugal fan, and more particularly to a double-layer fan impellerstructure of a centrifugal fan in which at least one layer of blades ofthe upper and lower layers is selectively arranged at unequal intervalsso as to lower the single tone of the blade passing frequency (BPF) andgreatly reduce noise.

2. Description of the Related Art

Along with the rapid development of electronic industries, theperformance of the electronic components has been more and moreenhanced. The electronic components have operated at higher and higherspeed. In the meantime, the heat generated by the electronic componentshas become higher and higher. In case the heat is not dissipated intime, the operation performance of the electronic components will bedeteriorated. In some more serious cases, the electronic components mayeven burn out. In order to dissipate the heat, a miniaturizedcentrifugal fan is installed in a limited space of the system forcarrying away the heat. The centrifugal fan includes a frame body, a fanhub and multiple blade bodies annularly disposed around outercircumference of the fan hub. Each of upper and lower sides of the framebody is formed with an air inlet. A lateral side of the frame body isformed with an air outlet. In operation, the blade bodies rotate todrive the ambient air to flow. The axial airflow going into the framebody from the air inlet is turned to radial airflow, which is exhaustedfrom the air outlet.

When the centrifugal fan operates, the non-uniform wake flowing out fromthe fan impeller will interact with the tongue to make noise. In thecase that the gap between the fan impeller and the tongue is relativelynarrow, the noise will be affected by the tongue oscillation caused bythe impact of the non-uniform wake onto the tongue and the pressuredifference around the tongue. In the case that the gap is 20% the radiusof the fan impeller, only the non-uniform wake will affect the majornoise source and the non-uniform wake only has little affection on themajor noise source. In addition, the wake strength can be lowered bymeans of adding short vanes between the blades. This can minimize theaffection of the non-uniform wake on the pressure turbulence and thenoise. According to the above, the conventional technique has thefollowing shortcomings:

-   1. The structural design is limited.-   2. The ratio of upper incoming air volume to lower incoming air    volume cannot be flexibly designed according to the characteristics.-   3. The noise is loud.

SUMMARY OF THE INVENTION

It is therefore a primary object of the present invention to provide afan impeller structure of centrifugal fan, which can effectively reducenoise.

To achieve the above and other objects, the fan impeller structure ofcentrifugal fan of the present invention includes a hub, a first bladebody set and a second blade body set.

The hub has an extension section. The extension section has a first sideand a second side. The first blade body set is disposed on the firstside. The first blade body set includes multiple first blade bodies. Thefirst blade bodies define therebetween multiple first air inlets andmultiple first air outlets. The first air outlets are arranged atunequal intervals. The second blade body set is disposed on the secondside. The second blade body set includes multiple second blade bodies.The second blade bodies define therebetween multiple second air inletsand multiple second air outlets. The second air outlets are arranged atequal intervals.

Still to achieve the above and other objects, the fan impeller structureof centrifugal fan of the present invention includes a hub, a firstblade body set and a second blade body set.

The hub has an extension section. The extension section has a first sideand a second side. The first blade body set is disposed on the firstside. The first blade body set includes multiple first blade bodies. Thefirst blade bodies define therebetween multiple first air inlets andmultiple first air outlets. The first air outlets are arranged atunequal intervals. The second blade body set is disposed on the secondside. The second blade body set includes multiple second blade bodies.The second blade bodies define therebetween multiple second air inletsand multiple second air outlets. The second air outlets are arranged atunequal intervals.

Still to achieve the above and other objects, the fan impeller structureof centrifugal fan of the present invention includes a hub, a firstblade body set and a second blade body set.

The hub has an extension section. The extension section has a first sideand a second side. The first blade body set is disposed on the firstside. The first blade body set includes multiple first blade bodies. Thefirst blade bodies define therebetween multiple first air inlets andmultiple first air outlets. The first air outlets are arranged at equalintervals. The second blade body set is disposed on the second side. Thesecond blade body set includes multiple second blade bodies. The secondblade bodies define therebetween multiple second air inlets and multiplesecond air outlets. The second air outlets are arranged at unequalintervals.

The first air outlets of the first blade body set or the second airoutlets of the second blade body set are selectively arranged at unequalintervals. This can lower the single tone of the blade passing frequency(BPF). Moreover, the double-layer fan impeller structure can increasethe blade passing frequency (BPF) and lower sound pressure weighting soas to greatly reduce noise. In addition, the upper and lower blades canbe more flexibly designed according to the boundary condition.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure and the technical means adopted by the present inventionto achieve the above and other objects can be best understood byreferring to the following detailed description of the preferredembodiments and the accompanying drawings, wherein:

FIG. 1 is a perspective view of a first embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 2 is a top view of the first embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 2 a is an enlarged view of circled area 2 a of FIG. 2;

FIG. 3 is a bottom view of the first embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 3 a is an enlarged view of circled area 3 a of FIG. 3.

FIG. 4 is a top view of a second embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 5 is a bottom view of the second embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 6 is a top view of a third embodiment of the fan impeller structureof centrifugal fan of the present invention;

FIG. 7 is a bottom view of the third embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 8 is a top view of a fourth embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 9 is a bottom view of the fourth embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 10 is a side view of a fifth embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 11 is a side view of a sixth embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 12 is a top view of a seventh embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 13 is a top view of an eighth embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 14 is a top view of a ninth embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 15 is a top view of a tenth embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 16 is a top view of an eleventh embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 17 is a top view of a twelfth embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 18 is a top view of a thirteenth embodiment of the fan impellerstructure of centrifugal fan of the present invention;

FIG. 19 is a top view of a fourteenth embodiment of the fan impellerstructure of centrifugal fan of the present invention; and

FIG. 20 is a top view of a fifteenth embodiment of the fan impellerstructure of centrifugal fan of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Please refer to FIGS. 1, 2, 2 a, 3 and 3 a. FIG. 1 is a perspective viewof a first embodiment of the fan impeller structure of centrifugal fanof the present invention. FIG. 2 is a top view of the first embodimentof the fan impeller structure of centrifugal fan of the presentinvention. FIG. 2 a is an enlarged view of circled area 2 a of FIG. 2.FIG. 3 is a bottom view of the first embodiment of the fan impellerstructure of centrifugal fan of the present invention. FIG. 3 a is anenlarged view of circled area 3 a of FIG. 3. According to the firstembodiment, the fan impeller structure 1 of centrifugal fan of thepresent invention includes a hub 11, a first blade body set 12 and asecond blade body set 13.

The hub 11 has an extension section 111 having a first side 1111 and asecond side 1112. The extension section 111 extends from thecircumference of the hub 11 in a direction away from the hub 11.

The first blade body set 12 is disposed on the first side 1111. Thefirst blade body set 12 includes multiple first blade bodies 121. Thefirst blade bodies 121 define therebetween multiple first air inlets 122and multiple first air outlets 123. The first air outlets 123 arearranged at unequal intervals.

The second blade body set 13 is disposed on the second side 1112. Thesecond blade body set 13 includes multiple second blade bodies 131. Thesecond blade bodies 131 define therebetween multiple second air inlets132 and multiple second air outlets 133. The second air outlets 133 arearranged at equal intervals.

The first blade body set 12 extends from the first side 1111 of theextension section 111 in a direction away from the hub 11. Each firstblade body 121 has a first end 1211 and a second end 1212. The first airinlet 122 is defined between the first ends 1211 of each two adjacentfirst blade bodies 121. The first air outlet 123 is defined between thesecond ends 1212 of each two adjacent first blade bodies 121. The secondblade body set 13 extends from the second side 1112 of the extensionsection 111 in a direction away from the hub 11. Each second blade body131 has a third end 1311 and a fourth end 1312. The second air inlet 132is defined between the third ends 1311 of each two adjacent second bladebodies 131. The second air outlet 133 is defined between the fourth ends1312 of each two adjacent second blade bodies 131.

The first ends 1211 together define a first pitch circle 124. A tangentof the first pitch circle 124 at the first end 1211 is defined as afirst tangent 125. The first blade body 121 has a first blade bodycentral line 1213. A tangent of the first blade body central line 1213at the first end 1211 is defined as a second tangent 126. The secondtangent 126 intersects the first tangent 125 to contain a first airincoming angle 12 a. The second ends 1212 together define a second pitchcircle 127. A tangent of the second pitch circle 127 at the second end1212 is defined as a third tangent 128. A tangent of the first bladebody central line 1213 at the second end 1212 is defined as a fourthtangent 129. The third tangent 128 and the fourth tangent 129 contain afirst air outgoing angle 12 b. The third ends 1311 together define athird pitch circle 134. A tangent of the third pitch circle 134 at thethird end 1311 is defined as a fifth tangent 135. The second blade body131 has a second blade body central line 1313. A tangent of the secondblade body central line 1313 at the third end 1311 is defined as a sixthtangent 136. The fifth tangent 135 intersects the sixth tangent 136 tocontain a second air incoming angle 13 a. The fourth ends 1312 togetherdefine a fourth pitch circle 137. A tangent of the fourth pitch circle137 at the fourth end 1312 is defined as a seventh tangent 138. Atangent of the second blade body central line 1313 at the fourth end1312 is defined as an eighth tangent 139. The seventh tangent 138 andthe eighth tangent 139 contain a second air outgoing angle 13 b. In thisembodiment, the first air incoming angle 12 a is larger than or equal tothe second air incoming angle 13 a.

The first blade body central line 1213 extends along the first bladebody 121 and has a curvature equal to that of the first blade body 121.The second blade body central line 1313 extends along the second bladebody 131 and has a curvature equal to that of the second blade body 131.The first blade body central line 1213 is a longitudinal central line ofthe thickness of the first blade body 121. That is, on the basis of thefirst blade body central line 1213, the widths extend from the firstblade body central line 1213 to two sides of the first blade body 121are equal to each other. Similarly, the second blade body central line1313 is a longitudinal central line of the thickness of the second bladebody 131. That is, on the basis of the second blade body central line1313, the widths extend from the second blade body central line 1313 totwo sides of the second blade body 131 are equal to each other.

Please now refer to FIGS. 4 and 5. FIG. 4 is a top view of a secondembodiment of the fan impeller structure of centrifugal fan of thepresent invention. FIG. 5 is a bottom view of the second embodiment ofthe fan impeller structure of centrifugal fan of the present invention.The second embodiment is partially identical to the first embodiment instructure and thus will not be repeatedly described hereinafter. Thesecond embodiment is different from the first embodiment in that thefirst air outgoing angle 12 b is smaller than or equal to the second airoutgoing angle 13 b.

Please now refer to FIGS. 6 and 7. FIG. 6 is a top view of a thirdembodiment of the fan impeller structure of centrifugal fan of thepresent invention. FIG. 7 is a bottom view of the third embodiment ofthe fan impeller structure of centrifugal fan of the present invention.The third embodiment is partially identical to the first embodiment instructure and thus will not be repeatedly described hereinafter. Thethird embodiment is different from the first embodiment in that thefirst air incoming angle 12 a is smaller than or equal to the second airincoming angle 13 a.

Please now refer to FIGS. 8 and 9. FIG. 8 is a top view of a fourthembodiment of the fan impeller structure of centrifugal fan of thepresent invention. FIG. 9 is a bottom view of the fourth embodiment ofthe fan impeller structure of centrifugal fan of the present invention.The fourth embodiment is partially identical to the first embodiment instructure and thus will not be repeatedly described hereinafter. Thefourth embodiment is different from the first embodiment in that thefirst air outgoing angle 12 b is larger than or equal to the second airoutgoing angle 13 b.

Please now refer to FIG. 10. FIG. 10 is a side view of a fifthembodiment of the fan impeller structure of centrifugal fan of thepresent invention. The fifth embodiment is partially identical to thefirst embodiment in structure and thus will not be repeatedly describedhereinafter. The fifth embodiment is different from the first embodimentin that the second end 1212 has a height larger than that of the fourthend 1312.

Please now refer to FIG. 11. FIG. 11 is a side view of a sixthembodiment of the fan impeller structure of centrifugal fan of thepresent invention. The sixth embodiment is partially identical to thefirst embodiment in structure and thus will not be repeatedly describedhereinafter. The sixth embodiment is different from the first embodimentin that the fourth end 1312 has a height larger than that of the secondend 1212.

Please now refer to FIG. 12. FIG. 12 is a top view of a seventhembodiment of the fan impeller structure of centrifugal fan of thepresent invention. The seventh embodiment is partially identical to thefirst embodiment in structure and thus will not be repeatedly describedhereinafter. The seventh embodiment is different from the firstembodiment in that the first blade body 121 has a length larger thanthat of the second blade body 131.

Please now refer to FIG. 13. FIG. 13 is a top view of an eighthembodiment of the fan impeller structure of centrifugal fan of thepresent invention. The eighth embodiment is partially identical to thefirst embodiment in structure and thus will not be repeatedly describedhereinafter. The eighth embodiment is different from the firstembodiment in that the second blade body 131 has a length larger thanthat of the first blade body 121.

Please now refer to FIG. 14. FIG. 14 is a top view of a ninth embodimentof the fan impeller structure of centrifugal fan of the presentinvention. The ninth embodiment is partially identical to the firstembodiment in structure and thus will not be repeatedly describedhereinafter. The ninth embodiment is different from the first embodimentin that the first end 1211 is aligned with the third end 1311, while thefirst and second air outlets 123, 133 are not aligned with each other.

Please now refer to FIG. 15. FIG. 14 is a top view of a tenth embodimentof the fan impeller structure of centrifugal fan of the presentinvention. The tenth embodiment is partially identical to the firstembodiment in structure and thus will not be repeatedly describedhereinafter. The tenth embodiment is different from the first embodimentin that the first end 1211 is not aligned with the third end 1311 andthe first and second air inlets 122, 132 are not aligned with eachother.

Please now refer to FIG. 16. FIG. 16 is a top view of an eleventhembodiment of the fan impeller structure of centrifugal fan of thepresent invention. The eleventh embodiment is partially identical to thetenth embodiment in structure and thus will not be repeatedly describedhereinafter. The eleventh embodiment is different from the tenthembodiment in that the first end 1211 is not aligned with the third end1311 and the first and second air inlets 122, 132 are not aligned witheach other.

Please now refer to FIG. 17. FIG. 17 is a top view of a twelfthembodiment of the fan impeller structure of centrifugal fan of thepresent invention. The twelfth embodiment is partially identical to thefirst embodiment in structure and thus will not be repeatedly describedhereinafter. The twelfth embodiment is different from the firstembodiment in that the number of the first blade bodies 121 is more thanthe number of the second blade bodies 131.

Please now refer to FIG. 18. FIG. 18 is a top view of a thirteenthembodiment of the fan impeller structure of centrifugal fan of thepresent invention. The thirteenth embodiment is partially identical tothe first embodiment in structure and thus will not be repeatedlydescribed hereinafter. The thirteenth embodiment is different from thefirst embodiment in that the number of the second blade bodies 131 ismore than the number of the first blade bodies 121.

Please now refer to FIG. 19. FIG. 19 is a top view of a fourteenthembodiment of the fan impeller structure of centrifugal fan of thepresent invention. The fourteenth embodiment is partially identical tothe first embodiment in structure and thus will not be repeatedlydescribed hereinafter. The fourteenth embodiment is different from thefirst embodiment in that the first air outlets 123 are arranged at equalintervals, while the second air outlets 133 are arranged at unequalintervals. The characteristic of this embodiment can be combined withthe characteristics of the second to thirteenth embodiments to achieveother aspects of the fan impeller structure.

Please now refer to FIG. 20. FIG. 20 is a top view of a fifteenthembodiment of the fan impeller structure of centrifugal fan of thepresent invention. The fifteenth embodiment is partially identical tothe first embodiment in structure and thus will not be repeatedlydescribed hereinafter. The fifteenth embodiment is different from thefirst embodiment in that the first air outlets 123 are arranged atunequal intervals and the second air outlets 133 are also arranged atunequal intervals. The characteristic of this embodiment can be combinedwith the characteristics of the second to thirteenth embodiments toachieve other aspects of the fan impeller structure.

The present invention has been described with the above embodimentsthereof and it is understood that many changes and modifications in theabove embodiments can be carried out without departing from the scopeand the spirit of the invention that is intended to be limited only bythe appended claims.

What is claimed is:
 1. A fan impeller structure of centrifugal fan, comprising: a hub having an extension section, the extension section having a first side and a second side; a first blade body set disposed on the first side, the first blade body set including multiple first blade bodies, the first blade bodies defining therebetween multiple first air inlets and multiple first air outlets, the first air outlets being arranged at unequal intervals; and a second blade body set disposed on the second side, the second blade body set including multiple second blade bodies, the second blade bodies defining therebetween multiple second air inlets and multiple second air outlets.
 2. The fan impeller structure of centrifugal fan as claimed in claim 1, wherein the first blade body set extends from the first side of the extension section in a direction away from the hub, each first blade body having a first end and a second end, the first air inlet being defined between the first ends of each two adjacent first blade bodies, the first air outlet being defined between the second ends of each two adjacent first blade bodies, the second blade body set extending from the second side of the extension section in a direction away from the hub, each second blade body having a third end and a fourth end, the second air inlet being defined between the third ends of each two adjacent second blade bodies, the second air outlet being defined between the fourth ends of each two adjacent second blade bodies.
 3. The fan impeller structure of centrifugal fan as claimed in claim 2, wherein the first ends together define a first pitch circle, a tangent of the first pitch circle at the first end being defined as a first tangent, the first blade body having a first blade body central line, a tangent of the first blade body central line at the first end being defined as a second tangent, the second tangent intersecting the first tangent to contain a first air incoming angle, the second ends together defining a second pitch circle, a tangent of the second pitch circle at the second end being defined as a third tangent, a tangent of the first blade body central line at the second end being defined as a fourth tangent, the third tangent and the fourth tangent containing a first air outgoing angle, the third ends together defining a third pitch circle, a tangent of the third pitch circle at the third end being defined as a fifth tangent, the second blade body having a second blade body central line, a tangent of the second blade body central line at the third end being defined as a sixth tangent, the fifth tangent intersecting the sixth tangent to contain a second air incoming angle, the fourth ends together defining a fourth pitch circle, a tangent of the fourth pitch circle at the fourth end being defined as a seventh tangent, a tangent of the second blade body central line at the fourth end being defined as an eighth tangent, the seventh tangent and the eighth tangent containing a second air outgoing angle.
 4. The fan impeller structure of centrifugal fan as claimed in claim 3, wherein the first air incoming angle is larger than or equal to the second air incoming angle.
 5. The fan impeller structure of centrifugal fan as claimed in claim 3, wherein the first air outgoing angle is larger than or equal to the second air outgoing angle.
 6. The fan impeller structure of centrifugal fan as claimed in claim 3, wherein the first air incoming angle is smaller than or equal to the second air incoming angle.
 7. The fan impeller structure of centrifugal fan as claimed in claim 3, wherein the first air outgoing angle is smaller than or equal to the second air outgoing angle.
 8. The fan impeller structure of centrifugal fan as claimed in claim 2, wherein the second end has a height larger than that of the fourth end.
 9. The fan impeller structure of centrifugal fan as claimed in claim 2, wherein the fourth end has a height larger than that of the second end.
 10. The fan impeller structure of centrifugal fan as claimed in claim 1, wherein the first blade body has a length larger than that of the second blade body.
 11. The fan impeller structure of centrifugal fan as claimed in claim 1, wherein the second blade body has a length larger than that of the first blade body.
 12. The fan impeller structure of centrifugal fan as claimed in claim 2, wherein the first end is aligned with the third end.
 13. The fan impeller structure of centrifugal fan as claimed in claim 3, wherein the first end is not aligned with the third end and the first and second air inlets are not aligned with each other.
 14. The fan impeller structure of centrifugal fan as claimed in claim 1, wherein the number of the first blade bodies is more than the number of the second blade bodies.
 15. The fan impeller structure of centrifugal fan as claimed in claim 1, wherein the number of the second blade bodies is more than the number of the first blade bodies.
 16. The fan impeller structure of centrifugal fan as claimed in claim 1, wherein the second blade bodies of the second blade body set are arranged at equal intervals or unequal intervals.
 17. A fan impeller structure of centrifugal fan, comprising: a hub having an extension section, the extension section having a first side and a second side; a first blade body set disposed on the first side, the first blade body set including multiple first blade bodies, the first blade bodies defining therebetween multiple first air inlets and multiple first air outlets, the first air outlets being arranged at equal intervals; and a second blade body set disposed on the second side, the second blade body set including multiple second blade bodies, the second blade bodies defining therebetween multiple second air inlets and multiple second air outlets, the second air outlets being arranged at unequal intervals.
 18. The fan impeller structure of centrifugal fan as claimed in claim 17, wherein the first blade body set extends from the first side of the extension section in a direction away from the hub, each first blade body having a first end and a second end, the first air inlet being defined between the first ends of each two adjacent first blade bodies, the first air outlet being defined between the second ends of each two adjacent first blade bodies, the second blade body set extending from the second side of the extension section in a direction away from the hub, each second blade body having a third end and a fourth end, the second air inlet being defined between the third ends of each two adjacent second blade bodies, the second air outlet being defined between the fourth ends of each two adjacent second blade bodies.
 19. The fan impeller structure of centrifugal fan as claimed in claim 18, wherein the first ends together define a first pitch circle, a tangent of the first pitch circle at the first end being defined as a first tangent, the first blade body having a first blade body central line, a tangent of the first blade body central line at the first end being defined as a second tangent, the second tangent intersecting the first tangent to contain a first air incoming angle, the second ends together defining a second pitch circle, a tangent of the second pitch circle at the second end being defined as a third tangent, a tangent of the first blade body central line at the second end being defined as a fourth tangent, the third tangent and the fourth tangent containing a first air outgoing angle, the third ends together defining a third pitch circle, a tangent of the third pitch circle at the third end being defined as a fifth tangent, the second blade body having a second blade body central line, a tangent of the second blade body central line at the third end being defined as a sixth tangent, the fifth tangent intersecting the sixth tangent to contain a second air incoming angle, the fourth ends together defining a fourth pitch circle, a tangent of the fourth pitch circle at the fourth end being defined as a seventh tangent, a tangent of the second blade body central line at the fourth end being defined as an eighth tangent, the seventh tangent and the eighth tangent containing a second air outgoing angle.
 20. The fan impeller structure of centrifugal fan as claimed in claim 19, wherein the first air incoming angle is larger than or equal to the second air incoming angle.
 21. The fan impeller structure of centrifugal fan as claimed in claim 19, wherein the first air outgoing angle is larger than or equal to the second air outgoing angle.
 22. The fan impeller structure of centrifugal fan as claimed in claim 19, wherein the first air incoming angle is smaller than or equal to the second air incoming angle.
 23. The fan impeller structure of centrifugal fan as claimed in claim 19, wherein the first air outgoing angle is smaller than or equal to the second air outgoing angle.
 24. The fan impeller structure of centrifugal fan as claimed in claim 18, wherein the second end has a height larger than that of the fourth end.
 25. The fan impeller structure of centrifugal fan as claimed in claim 18, wherein the fourth end has a height larger than that of the second end.
 26. The fan impeller structure of centrifugal fan as claimed in claim 17, wherein the first blade body has a length larger than that of the second blade body.
 27. The fan impeller structure of centrifugal fan as claimed in claim 17, wherein the second blade body has a length larger than that of the first blade body.
 28. The fan impeller structure of centrifugal fan as claimed in claim 18, wherein the first end is aligned with the third end.
 29. The fan impeller structure of centrifugal fan as claimed in claim 19, wherein the first end is not aligned with the third end and the first and second air inlets are not aligned with each other.
 30. The fan impeller structure of centrifugal fan as claimed in claim 17, wherein the number of the first blade bodies is more than the number of the second blade bodies.
 31. The fan impeller structure of centrifugal fan as claimed in claim 17, wherein the number of the second blade bodies is more than the number of the first blade bodies. 